1. Field of the Invention:
The present invention relates to a hot/cold water mixing device, and more particularly to a hot/cold water mixing device including a hot water supply valve and a cold water supply valve which can mechanically or operatively be opened and closed in a complementary fashion, the speeds of opening and closing of the supply valves being determined on the difference between the actual temperature of hot water flowing out of a water outlet and a desired hot water temperature.
2. Description of the Relevant art:
There is known a hot/cold water mixing device for discharging hot water at a desired temperature To from the faucet of a bathtub, for example, the hot/cold water mixing device having a hot water supply valve and a cold water supply valve which can mechanically or operatively be opened and closed complementarily, the speeds of opening and closing of the supply valves being determined dT on the difference between the actual measured temperature Tm of the hot water flowing out of the faucet and the desired hot water temperature To. The hot water supply valve is disposed between a source of relatively hot water and the faucet, and the cold water supply valve is disposed between a source of relatively cold water and the faucet. In reality, the valves are held in communication with the faucet through a water mixture pipe. The hot/cold water mixing device has an improved capability for making hte measured temperature Tm to be highly responsive to the desired temperature To set by the operator.
More specifically, the hot water supply valve and the cold water supply valve are mechanically interlinked such that when one of the valves is driven so as to be closed at a certain speed R, the other valve is simultaneously driven so as to be opened at a speed - R. The amount of hot water supplied to the bathtub is set at will by the operator, and cannot be controlled by the hot/cold water mixing device. In practice, the hot water source and the cold water source are connected to a hot water faucet in a kitchen through another hot/cold water mixing device of identical design. The hot/cold water mixing device has a mechanism for determining the speed R in order to provide a prescribed gain with respect to the difference dT, and a drive mechanism for opening and closing the hot water supply valve and the cold water supply valve in an interlinked fashion based on the determined speed R. The speed determining mechanism is in the form of a one-chip microcomputer having a CPU, a RAM, a ROM, and other integral components. The prescribed gain is of a relatively small value in order to prevent the valve drive mechanism from hunting in the neighborhood of the desired temperature To. The speeds R, - R of opening and closing the valves are determined in proportion to the difference dT. Therefore, the response of the measured temperature Tm to the desired temperature To in the hot/cold water mixing device is better than that in an early hot/cold water mixing device of the type in which the hot water supply valve and the cold water supply valve are opened and closed in an interlinked manner at a constant speed irrespective of the difference dT. The condition in which the measured temperature Tm remains substantially equal to the desired temperature To over a certain period of time is referred to as a stable hot water discharge condition.
Since the gain referred to above is of a relativley small value, a relatively high valve opening and closing speed R is not attained even when the measured temperature Tm is varied due to an abrupt change in the pressure of water from the hot or cold water source during the stable hot-water temperature condition. One example of such an abrupt change in the pressure of water from the hot water source may be a pressure buildup caused when a higher setting is given for the desired temperature To and the hot water faucet in a kitchen that has been open is abruptly closed. When this happens, therefore, a relatively long interval of time is required until the measured temperature Tm in the hot/cold water mixing device for a bathtub returns to the desired temperature To. This problem could be solved by setting a relativley large value for the above gain. However, the valve drive mechanism and hence the measured temperature Tm would tend to suffer hunting in the vicinity of the desired temperature To.
The present invention has been made in an effort to eliminate the aforesaid drawbacks of the conventional hot/cold water mixing device.